The present invention relates to a multi-axis machine tool of which the essential features are recited in the preamble of claim 1 appended.
More particularly, the invention is pertinent to the art field of numerically controlled multi-axis machine tools used to perform high-speed milling operations.
Conventionally, such machine tools are utilized particularly in the aerospace industries for contouring and drilling parts made of aluminum and composite materials, and in the automobile sector for producing master models, models for bodywork, internal parts and dies.
Multi-axis machines of the type in question comprise a frame, or gantry, composed of two upright members with first ends anchored slidably or otherwise to the bed of the machine, and a horizontal cross member extending between and rigidly associated with the second ends of the two upright members.
Such machines also comprise a moving horizontal member, or beam, sliding on the upright members and consequently positionable closer to or farther from the bed. The bed affords a machining station to which the workpiece is secured.
The moving beam is coupled slidably by its two opposite ends to the upright members and serves to support a carriage, traversable horizontally along the beam. The carriage in turn carries a machining head with a tool holder, to which the tool best suited to the machining operation is clamped.
More particularly, a first conventional type of multi-axis machine is equipped with a tool holder having one degree of freedom, namely rotational, relative to the carriage traversable horizontally along the moving beam.
In this instance, the machining station has two degrees of freedom relative to the gantry of the machine tool, in that the station is translatable and rotatable with respect to the gantry.
Accordingly, the machine tool has five degrees of freedom and is able to perform the requisite operations on the workpiece correctly.
In reality however, machine tools of this type will not allow particularly large workpieces to be processed, given that during the rotation of the machining station, such bulky items would interfere with the uprights of the gantry and effectively prevent the work from being positioned correctly in relation to the tool holder.
In another conventional type of machine tool, the tool holder has two degrees of freedom relative to the carriage traversable horizontally along the moving beam.
In particular, the tool holder is mounted to a quill extendible along a vertical axis relative to the carriage and rotatable about this same vertical axis.
In this instance, the machining station possesses just one degree of freedom relative to the gantry, consisting in relative translational motion between gantry and station.
Accordingly, the machine tool has five degrees of freedom and is able to perform the requisite operations on the workpiece correctly.
With this second type of design, however, the rigidity of the connection between tool and machine is afforded by the rigidity of the quill, and since the rigidity of the quill when extended from the carriage is decidedly low, when compared to that of the carriage and the moving beam, high machining accuracy cannot be guaranteed.
Moreover, because the rigidity in question is dependent on the portion of the quill projecting from the carriage, the load transmissible from the tool to the workpiece compatible with a given level of machining accuracy can never be constant, as the maximum load applicable to the work in machining has to be calculated on the basis of the distance the quill is extended from the tool carriage.
The applicant finds that multi-axis machine tools of the prior art are improvable in a number of ways, with regard particularly to the accuracy and flexibility in machining of which they are capable.
In the light of the foregoing, the main object of the present invention is to provide a multi-axis machine tool unaffected by the drawbacks mentioned.
In particular, the object of the invention is to set forth a multi-axis machine tool capable of high machining accuracy.
A further object of the present invention is to set forth a multi-axis machine tool able to process workpieces of sizeable proportions.